1. Field of the Invention
The present invention relates to an optical recording medium driving apparatus and an optical recording medium driving method, and is suitably applied, for example, to an optical disc driving apparatus.
2. Description of the Related Art
As an optical disc driving apparatus, one that is configured to irradiate a light beam to an optical disc as a recording medium and thereby recording information to the optical disc or reproducing information from the optical disc has been widely used.
Among the optical disc driving apparatuses, one that is compatible with both an optical disc of a compact disc (CD) system in which a light beam of a wavelength of around 780 nm is used, and an optical disc of a digital versatile disc (DVD) system in which an light beam of a wavelength of around 660 nm is used has been suggested.
Further, optical discs commonly have a disc shape with an external diameter of around 120 mm and a thickness of around 1.2 mm in both the CD system and the DVD system. However, a space from a front surface of the optical disc to a recording layer thereof where information is recorded, that is, a thickness of a so-called cover layer, is different in both systems, and is around 1.2 mm in the CD system and around 0.6 mm in the DVD system.
Moreover, with respect to the optical driving apparatus as well, a numerical aperture (NA) of an objective lens that irradiates an light beam to the optical disc is specified, and a numerical aperture for the optical disc of the CD system needs to be 0.45 and a numerical aperture for the optical disc of the DVD system needs to be 0.6.
Under the circumstances, among the optical disc driving apparatuses, one that is compatible with the optical discs of both the CD system and the DVD system by using a bifocal objective lens having two focuses has been suggested.
Such an optical disc driving apparatus uses a method of recognizing a space between a front surface of the optical disc and a recording layer thereof based on, for example, a result of detection of a reflected light beam obtained by irradiation of a light beam on the optical disc, when the optical disc is loaded, in order to determine a type of the optical disc from the CD system or the DVD system based on the space, and of properly focusing the light beam on the recording layer. At this time, the optical disc driving apparatus can exclude a reflected light beam component that is obtained by a false focus which is not a desired focus among focuses of the light beam (for example, refer to Jpn. Pat. Appln. Laid-Open Publication No. 2003-157545 [FIG. 2]).